1. Field of the Invention
This invention relates to a method for making a relief pattern of a cured resin on a transparent colored layer by the use of a photocurable or photocrosslinking material or composition. This method may be applied to the fabrication of a color filter for liquid crystal displays in which a relief pattern is formed on color pixels of a the transparent colored layer of the filter.
2. Description of the Prior Art
As is known in the art, a liquid crystal used in a liquid crystal display has an inherent refraction anisotropy. In order to obtain high quality full-color LTV images, it is essential that the display have a multi-gap structure with optimum cell gaps for the respective red, green and blue color pixels.
In prior art processes of making a color filter having such a multi-gap structure, it is usual to apply a dyeing photosensitive material, such as modified proteins or synthetic dyeing resins sensitized with dichromates or diazonium salts, onto a glass substrate and to subject the applied material to patterning, after which the resultant patterned layers are, respectively, dyed with dye solutions, i.e. the dyeing procedure is repeated three times to make red, green and blue color pixels. In this connection, however, the respective pixels must be properly controlled in thickness. This is usually made by finely controlling a coating amount of the dyeing photosensitive material on the glass substrate. However, such a fine control is very difficult because of the swelling of the resin after dyeing, thus presenting the problem that the thicknesses of the respective pixels can rarely be controlled as desired.
For the formation of a stepped relief on the transparent colored layer composed of the color pixels, photocurable or photocrosslinking polymers or compositions are used. In general, the types of the polymers or compositions can be broadly classified as follows.
(1) A photosensitive material is used and excited by absorption of light and acts on a dispersion polymer medium to harden the polymer by crosslinkage.
(2) If satisfactory sensitivity cannot be obtained by the use of a photo-crosslinking agent alone, a sensitizer is used by mixing with the photo-crosslinking agent. The photo-crosslinking agent is excited by occurrence of energy transfer from the sensitizer toward the photo-crosslinking agent and reacts with polymer chains. PG,4
(3) Polymers having a photosensitive group are used and this group is optically excited and combined with other functional groups.
(4) The polymers in (3) are used in combination with sensitizers to facilitate the photo-excitation.
With (1) and (2), the spectral sensitivity for the photo curing corresponds substantially to the absorption spectrum of a photosensitive material or a photosensitive group. With (2) and (4), the spectral sensitivity is determined by combination of a photosensitive material and a sensitizer. Accordingly, it is necessary that the control of the spectral sensitivity of a photosensitive resin be made by proper selection of a photosensitive material or by addition of an appropriate type of dye sensitizer.
Nevertheless, it is not possible to arbitrarily change the spectral sensitivity and thus, it has not been possible to form on the surface of a colored transparent layer a desired relief pattern corresponding to a visible transmission spectrum.